This invention relates to thermoplastic containers for the retention of fluids under pressure, such as carbonated beverages and the like. These containers may be prepared from a preform or parison which may be injection molded, followed by blow molding said parison into a suitably shaped container. A typical thermoplastic material is poly (ethylene terephthalate) or PET, although others can be used.
The container configuration generally includes a neck portion with a cap-receiving means, a shoulder portion depending therefrom, a side wall or main body portion depending from the shoulder portion and a bottom wall joined to the side wall. In many of these containers the bottom wall has a champagne bottle bottom configuration with an internal, axially inwardly directed, generally conical part.
The bottom wall of these containers represents a weak part of the container. Also, it is desirable to provide a bottom shape capable of serving as a bottom support.
Thus, beverage under pressure within the container has a tendency to deform the bottom wall, as for example inverting the inwardly directed conical part to render the bottom wall unstable.
Many attempts have been made to overcome these problems while at the same time providing a construction which is inexpensive and economical to process. For example, U.S. Pat. No. 3,881,621 provides a ribbed strengthening at the bottom wall; however, this still provides insufficient strengthening. U.S. Pat. No. 4,134,510 provides a plurality of concentric annular strengthening ribs and a plurality of additional intersecting radial ribs in a complex and expensive procedure. U.S. Pat. Nos. 4,620,639, 4,261,948, 4,603,831, and 4,334,627 utilize a plurality of inwardly projecting rigid ribs so that the bottom wall is thicker at the ribbed portion than the remainder of the bottom wall; however, this results in a container having substantial and sharply defined differences in wall thickness with resultant sharp temperature differences in processing presenting difficult processing control problems.
Copending U.S. patent application Ser. No. 044,469, By Herbert Strassheimer, teaches an improved plastic preform for forming blow molded plastic containers and resultant improved plastic containers wherein the container has a tubular body portion adjacent a bottom portion and extending onto the bottom portion having circumferentially spaced radially extending continuous alterations in wall thickness. The preform is characterized by the bottom structure thereof having a plurality of flat faces capable of forming a blow molded plastic bottle with a bottom portion having said circumferentially spaced radially extending continuous alterations in wall thickness with a regularly undulating cross section across the circumference thereof, wherein said alterations in wall thickness are progressive and gradual. The teaching of said copending application Ser. No. 044,469 provides a stable and reinforced bottom wall configuration which is simple in construction and inexpensive to prepare and a preform which is similarly convenient and expeditious to prepare. However, it is desirable to further improve the characteristics of the resultant container, especially the resultant bottom regions corresponding to the corners between the flat faces of the preform. It is highly desirable to enhance the properties at this region and increase local orientation.
It is therefore a principal object of the present invention to provide an improved plastic preform and an improved thermoplastic container prepared therefrom having a stable and reinforced bottom wall configuration.
It is a further object of the present invention to provide an improved preform and container as aforesaid which is simple in construction and inexpensive to prepare.
Further objects and advantages of the present invention will appear hereinbelow.